1. Field of the Invention
The present invention relates, in general, to the field of fastening tools. In particular, the present invention relates to fastening tools having plural sources of power channeled through plural handles, and more particularly to a fastening tool for industrial applications such as the manufacture of pallets, used in the shipping and handling of commercial of goods.
Pallets are constructed by assembling wood boards in the form of a frame having at least one, and normally two, supporting surfaces or platforms which are spaced by beams or runners which extend perpendicular to the supporting surfaces in spaced relation. In the manufacture of wooden pallets, the boards which form the supporting surfaces at both the top and bottom of the pallet are spaced at desired intervals along such surface and fastened to the beams or runners to form a rigid frame assembly. In addition to wood, pallets can be made from plastic, metal, and paper. Fastening tools are used to join boards together to form a pallet.
2. Description of the Related Art
Pneumatic fastening tool development has been directed toward designing fastening tools that are for use with one hand. Therefore, a movement in the pneumatic fastening tool field is to design new tools that are smaller and lighter in weight, yet still maintain the driving power of traditional and older pneumatic fastening tools. The design of lightweight pneumatic fastening tools for single-handed fastening is in response to tool users' need to position, with their free hand, workpieces to be fastened together.
In industrial environments, however, such as the pallet fabrication and repair industry, the user does not need to use their free hand to position workpieces to be fastened together, because workpieces are arranged through automation. As a result, the free hand is idle and at risk of injury or being involved in a workplace accident, as the free hand is not required for use in the industrial fabrication operation. Adding a second handle that provides a control mechanism for operation of the tool requires both hands to be on the tool, thereby reducing the risk of injury in an industrial workplace accident.
A second handle has been used on existing large or heavy hand-held pneumatic fastening tools so that both hands of the user can be used to balance the tool and position the tool more easily. However, as a second handle is not required for actual operation, these existing tools can be operated with a single hand. A second handle for balancing the tool that is not required for operating the tool, is generally referred to as a “dead” handle. Dead handles do not require that both hands be on the tool for operation of the tool.
Taiwan Patent Application No. 1352652, which is herein incorporated by reference in its entirety, discloses a tool 1000 having a first handle 1002 and a second 1004 that controls air supply into the fastening tool for operation of the tool. Such an active second handle 1004 is generally referred to as a “live” handle. The second handle 1004, as shown in FIG. 1, is a live handle located in the air supply path of the tool and includes a manually operated pneumatic valve controlled by a lever 1006 that renders the tool non-operational unless the second handle 1004 is grasped and the lever 1006 is pulled to activate the valve. The valve opens to supply compressed air into the tool. FIG. 2 is a functional schematic of the tool operation with the second handle 1004. The schematic shows how the tool activation is dependent upon both of the users' hands controlling two separate valves in addition to engaging the work contact element with the workpiece to operate the tool 1000. The two separate valves are a first handle trigger valve 1008 and a second handle trigger valve 1010.
One of the challenges of having an auxiliary handle is providing a sufficient supply of compressed air to the tool for operation with varying air system environments and fastening rates. The live handle must be designed so that the force to activate the valve is within a range that is not fatiguing to the user. Also, the live handle body must be ergonomically designed to reduce grasp fatigue. The above design considerations result in an upper limit to the air flow rate through the auxiliary handle which can lead to functional problems when a higher air flow rate is required.
The functional schematic of FIG. 2 shows the external connections between elements of the fastener assembly shown in FIG. 1. When the live handle is released, the volume of compressed air in the tool reservoir 1012 is completely exhausted. As a result, the tool 1000 has a higher air consumption necessitating a higher capacity air compressor.